Calcium significantly improves the fruit quality of red-flesh ‘Hongyang’ kiwifruit

Abstract Red-flesh kiwifruit is very interesting to customers; however, several defaults affect its commercial cultivation, including small fruit size, cavities, environmental sensitivity of the skin and short shelf life, among others. In this study, we aimed to explore the effects of calcium on the fruit quality of Actinidia chinensis cv. Hongyang, a popular red-flesh cultivar, these inclueded different forms of calcium and methodologies (application time and frequency of the exogenous application). Additionally, a reverse control group treated with calcium antagonist chlorpromazine (CPZ) was established. The systematic studies indicated that applying the chelated calcium (EDTA-Ca) solution twice on the surface of the fruit significantly improved fruit weight and extended the storage period of 'Hongyang'. The fruit weight increased to 112.62 g, and the storage period at room temperature was extended to 12 days. It also significantly increased fruit dry matter (up to 20.67%), soluble sugar content (11.08 mg/g) and calcium content (170.95 μg/g); the increase in dry matter and soluble solid content improved the fruit’s taste. A comprehensive evaluation of all the related functional values and principal component analysis revealed that the highest comprehensive score (5.09) of fruit quality of 'Hongyang' fruit was achieved after two applications of EDTA-Ca solution by fruit surface immersion. In contrast, foliar application of calcium showed no significant improvement of fruit calcium content. Overall, a comprehensive analysis showed that EDTA-Ca achieved a better comprehensive result than Ca(NO 3 ) 2 . Fruit dipping yielded the best results, foliar spraying was better than root treated, and two applications were better than only one time of application. This research provides theoretical support for the rational application of exogenous calcium in 'Hongyang' kiwifruit. It significantly improves ‘Hongyang’ fruit quality and production while extending its storage time. Significance of the study What is already known on this subject? Previous research has established the importance of calcium in fruit development and quality, particularly in enhancing firmness, reducing physiological disorders and extending shelf life. Various methods of calcium application, such as foliar sprays and soil amendments, have been explored, but their relative effectiveness on specific fruit varieties, including kiwifruit, has not been thoroughly compared. What are the new findings? This study reveals that calcium soaking on the fruit surface is more effective than foliar calcium spraying. Additionally, chelated calcium outperforms inorganic calcium, with the combination of two soaking methods yielding the best results. These methods significantly increase single fruit weight, storage duration, soluble sugar content, calcium content and dry matter content in kiwifruit while also reducing the rate of fruit deformity. What are the expected impacts on horticulture? The findings of this research offer valuable theoretical support for the efficient use of exogenous calcium in kiwifruit and potentially other berry crops. By improving the quality of ‘Hongyang’ kiwifruit and extending its storage life, these practices can enhance marketability and reduce postharvest losses, ultimately benefiting growers and the horticultural industry as a whole.